The present invention relates to vehicle drivelines coupled to engines, and more particularly to drivelines including a planetary gear transmission and a damper assembly coupled to an engine.
Vehicle transmissions have typically been one of two types. There are manual transmissions, which, while more fuel efficient, require significant effort by the operator. They also generally allow more engine noise and vibration created by the engine to transfer through to the transmission and other driveline components, which is generally undesirable to the vehicle occupants. Some have tried to reduce the transmission of vibrations and noise by employing a dual mass flywheel, connected to the engine output, in which the two masses are connected by a radial spring assembly and a friction damper. But, while improving the vibration and noise transmission somewhat, it is limited in the range of transient vibrations that it can handle. Generally, the spring/friction damper assembly can only be tuned for a limited range of engine events. For example, if tuned for damping torque spikes from the engine, then it does not damp sufficiently for single firing impulses from the engine. Moreover, these systems are still coupled to a manual transmission, with all of its inconveniences.
On the other hand, there are automatic transmissions, which, while they are very convenient for the operator of the vehicle, are less fuel efficient. One of the reasons that the automatic transmissions are less efficient is that they employ a torque converter to transfer the torque output from the engine to the input of the transmission. The torque converter allows the vehicle to stop and start while in gear without stalling the engine. It also provides the added benefit of isolating the engine pulsations from the transmission, thus providing for a smoother operating drivetrain with less noise. Even if the torque converter includes a lock-up clutch for higher speed operation, the lock up clutch typically has some type of basic damper on it to provide isolation of the noise and vibrations transmitted from the engine although it does not need to be particularly good at damping over broad ranges since the converter locks up under only limited conditions. The torque converter, in particular, damps noise and vibrations during transients in the torque, such as lug limits at low RPMs, accelerator pedal tip-in, shifting between gears, and initial start-up of the vehicle.
With today""s ever increasing desires for improved fuel economy in vehicles, however, the inefficiencies inherent in a torque converter driven automatic transmission are undesirable. So, automatic transmission systems (i.e., typical planetary gear sets) are being developed where the torque converter is eliminated. In its place, a wet clutch, or other mechanism, is employed to allow for both vehicle start up and also the vehicle remaining stopped while the automatic transmission is in gear. This type of transmission is sometimes referred to as a powershift transmission. Thus, the automatic transmission operates with the convenience that vehicle operators prefer while improving fuel economy.
But the secondary benefit that the torque converter provided, namely isolation of the engine pulsations from the automatic transmission, is now eliminated.
Thus, it is desirable to have a powershift transmission that provides the improved fuel economy of a drivetrain that operates without a torque converter, yet still provides isolation of the transmission from the noise and vibrations, of various types, of the engine. Further, it is desirable that the isolation assembly is small and light weight to maximize the fuel efficiency and packaging gains achieved from removing a torque converter.
In its embodiments, the present invention contemplates an isolation assembly for use with an engine and a planetary transmission. The isolation assembly includes an input assembly adapted to be rotationally coupled to the engine, and an output assembly adapted to be rotationally coupled to the transmission and adjacent the input assembly to form a cavity therebetween. A plurality of generally radially oriented spring assemblies have a first radially inner end coupled to one of the input assembly and the output assembly, and a second radially outer end coupled to the other of the input assembly and the output assembly. Also, the isolation assembly includes a viscous damper having a viscous fluid within the cavity.
The present invention further contemplates a method of providing vibrational torque isolation between and engine, having an output member with a torque applied from the engine, and a planetary gear set transmission, having an input member, the method comprising the steps of: coupling the engine output member to an input element of a radial spring assembly; transferring torque through the radial spring assembly; coupling an output of the radial spring assembly to the transmission input member; coupling the engine output member to an input of a viscous fluid damper assembly; transferring torque through the viscous fluid damper assembly; and coupling an output of the viscous fluid damper assembly to the transmission input member.
Accordingly, an object of the present invention is to provide isolation between an engine and an automatic transmission, in a vehicle driveline that does not employ a torque converter.
Another object of the present invention is to provide an isolation assembly with a low spring rate, long travel springs and a viscous damper as a single, compact, light weight, unit.
An advantage of the present invention is that a vehicle""s fuel efficiency can be improved without transmitting unwanted noise and vibration to vehicle occupants.
Another advantage of the present invention is that long travel, low spring rate springs will allow for effective torque transfer while minimizing noise and vibration transferred through an isolation assembly.
A further advantage of the present invention is that a viscous fluid damper in the isolation assembly will allow for rate dependent damping, thereby reducing transmission of noise and vibration over a wide range of frequencies.